A plasma treatment process and a plasma processing apparatus are the technology indispensable in manufacturing of a overly fine semiconductor device, and in manufacturing of a high resolution plane display device containing a liquid crystal display device of having a gate length of 0.1 μm or not greater than 0.1 μm, what is called a deep submicron element or a deep subquarter micron element in recent years.
Although an excitation method of more various plasma than before is used as a plasma processing apparatus used for manufacturing of a semiconductor device or a liquid crystal display device, a parallel monotonous type high frequency excitation plasma processing apparatus or an inductively-coupled plasma processing apparatus is especially common. However, plasma formation by a conventional plasma processing apparatus is uneven, and an area with high electron density is limited. Therefore, there is a problem of difficulty in performing a uniform process over the whole surface of the substrate to be processed with a high processing rate, namely, a throughput. This problem becomes particularly serious in cases when a substrate having a large diameter is processed. And in the conventional plasma processing apparatus, since electron temperature is high, a semiconductor device formed on a substrate to be processed was damaged. The conventional plasma processing apparatus also has some essential problems such as metal contamination by sputtering of a processing chamber wall is large. Therefore, the conventional plasma processing apparatus is becoming difficult to satisfy a severe requirement against the further refinement of a semiconductor device or a liquid crystal display device and improvement in further productivity.
On the other hand, a microwave plasma processing apparatus using high-density plasma excited by microwave electric field without using a direct-current magnetic field has been conventionally proposed. For example, a plasma processing apparatus having a structure for radiating microwave into a processing chamber from a planate antenna (radial line slot antenna), which has a large number of slots arranged to generate uniform microwave, for ionizing gas in a processing chamber by this microwave electric field and for exciting plasma is proposed (refer to the Patent reference No. 1). In microwave plasma excited by such technique, it is possible to realize high plasma density over a wide area directly under the antenna and to perform uniform plasma processing for a short time. And in microwave plasma formed by this technique, electron temperature is low because the plasma is excited by microwave, and damage and metal contamination of a surface to be processed can be avoided. Since uniform plasma can easily be excited also on a large area over the substrate, it can also be applied easily to a manufacturing process of a semiconductor device and a manufacturing of a large-sized liquid crystal display device using a semiconductor substrate of a large diameter.
In these plasma processing apparatuses, a shower plate provided with a plurality of longitudinal holes as a gas releasing path is usually used in order to supply gas for plasma excitation uniformly in a processing chamber. However, plasma formed directly under the shower plate may flow backwards into a longitudinal hole of the shower plate by use of the shower plate. When plasma flows backwards into the longitudinal hole, there is a problem that abnormal electric discharge and deposition of gas will occur and degradation of transmission efficiency of microwave for exciting plasma and a decline of yield will occur.
Many improvements of structure of the shower plate are proposed as a method for preventing a back-flow of this plasma into the longitudinal hole.
For example, Patent reference No. 2 discloses that it is effective to structure an aperture of a gas discharge hole arranged at the edge of the longitudinal hole to be less than two times of a sheath thickness of plasma formed directly under the shower plate. However, just making the aperture of the gas discharge hole small is not sufficient enough as a method to prevent the back-flow of plasma. Particularly, when increasing plasma density from a conventional value of about 1012 cm−3 to about 1013 cm−3 in order to reduce a damage and increase a processing rate, the back-flow of plasma becomes remarkable and the back-flow of plasma cannot be prevented only by controlling the aperture of the gas discharge hole. It is also difficult to form a gas discharge hole of a fine aperture in the shower plate body by hole processing, and there is also a problem of processability.
Patent reference No. 3 suggests the use of the shower plate formed by a sintered porous-ceramic body having air permeability. This tends to prevent an back-flow of plasma with a wall of many pores, which structures the sintered porous-ceramic body.
However, the shower plate, which is formed by this general sintered porous-ceramic body sintered at normal temperature and normal pressure has a large variation in the pore diameter from about several μm to several tens μm. Since a diameter of the maximum crystal is as large as about 20 μm and the texture is not uniform, when surface flatness is bad and the surface, which is exposed to plasma, is formed by the sintered porous-ceramic body, effective surface area will increase. Therefore, re-combining of an electron and ion of plasma increases, and there is a problem that electric power efficiency of plasma excitation is bad. Here, the above-mentioned patent reference 3 discloses a structure for forming an opening for gas discharge in the shower plate, which is structured by a fine alumina, attaching the general sintered porous-ceramic body sintered at normal temperature and normal pressure onto this opening and emitting gas via this sintered porous-ceramic body, instead of configuring the whole shower plate from a sintered porous-ceramic body. However, in this structure, since a general sintered porous-ceramic body sintered at normal temperature and normal pressure is used, the above-mentioned problem generated from badness of surface flatness is not solved.
Previously, in patent reference 4, applicant for this patent proposed a method for preventing a back-flow of plasma by adjustment of a diameter size of a gas discharge hole, instead of changing a structure of a shower plate. That is, while preventing the back-flow of plasma by a diameter of a gas discharge hole being less than 0.1-0.3 mm, and moreover making the diameter dimensional tolerance into accuracy of less than ±0.002 mm, variation of a discharge volume of gas is abolished.
However, when this shower plate was actually used with a microwave plasma processing apparatus on conditions in which the plasma density was increased to 1013 cm−3, a light brown discoloration portion appeared as shown in FIG. 21. The cause of the light brown discoloration seems to be the back-flow of plasma into a space 602, into which the gas for plasma excitation is filled, which is formed between a shower plate body 600 and a cover plate 601, and the back-flow of plasma into a longitudinal hole 603 that communicates with the space 602, or is seemed to be the ignition on the gas for plasma excitation in sections of the space 602 and the longitudinal hole 603.    Patent reference No. 1: Japanese Patent Application Publication No. H09-63793    Patent reference No. 2: Japanese Patent Application Publication No. 2005-33167    Patent reference No. 3: Japanese Patent Application Publication No. 2004-39972    Patent reference No. 4: The international publication 06th/No. 112392 pamphlet